Paving of roads and parking lots with asphalt is a mature prior art. Typically, asphalt paving medium (referred to herein as “asphalt”) is prepared in a batch plant wherein a crushed stone aggregate is mixed with a hot tar preparation, yielding a highly viscous slurry of aggregate in tar that can be poured or laid in a layer onto a designated paving surface and then worked by specialized equipment to provide a durable surface for vehicular traffic when cool.
Hot asphalt, as it comes from the plant and is laid in a layer, contains significant amounts of entrained air and is in a non-compressed state. Thus paving comprises at least three distinct steps: a) laying the asphalt slurry in a layer of approximately the final thickness and lateral distribution; and finishing the layer by b) compacting the layer to remove air and ensure compaction into any depressions in the underlying substrate surface, and c) final smoothing of the compacted layer.
Once the designated surface is prepared to receive the asphalt, the first step of laying the asphalt is typically carried out by a laying machine that receives sequential batches of hot asphalt from delivery trucks and dispenses a continuous ribbon of the material while moving along the surface to be paved. In irregular areas such as parking lots, the distribution may be augmented manually by workers with shovels and/or screeds.
The second step of compacting the asphalt typically is carried out by a compacting machine that travels on one or more sets of smooth-surface, ganged rubber tires and that propels itself along the freshly-laid layer of hot asphalt. The tires are independently suspended in pairs such that the gangs of tires may follow the contours of the underlying surface to compact the asphalt in surface depressions as well as in the higher surface areas. This is an important step in assuring a long-wearing finished surface; failure to compact the material properly in depressions can result in development of potholes and premature failure of the finished layer.
The third step of smoothing the asphalt typically is carried out by a smoothing machine that travels on one or more smooth-surface steel rollers and that propels itself along the freshly-compacted layer of hot asphalt. The steel rollers work the compacted asphalt both forwardly and laterally to eliminate depressions and thus provide an overall even layer. In addition, the steel rollers intensely compact the upper part of the layer to impart a very fine-grained surface finish to the layer.
After the smoothing operation, the finished asphalt layer is allowed to cool and solidify, preferably before vehicular traffic is allowed onto the surface.
A shortcoming of the prior art is that two separate finishing machines are required for compacting and smoothing, respectively. These prior art machines, while very similar in overall construction and operation, are equipped with rubber tires and steel rollers, respectively. Each machine, even modest versions thereof, may cost in excess of $100,000, making ownership of both such machines prohibitive for many smaller paving companies; instead, one or both machines typically is/are rented for specific paving jobs, which entails rental fees, and coordinating rental and construction schedules, and machine transportation to and from the paving site. Further, as a paving business grows and the purchase of paving machines becomes feasible, each additional increment of production capacity requires the purchase of two finishing machines, one of each type.
What is needed in the art is an improvement whereby only one compacting and smoothing finishing machine is required for a paving operation.
It is a principal object of the present invention to reduce the cost of buying or renting finishing machines for an asphalt paving contractor.
It is a further object of the invention to simplify the logistics and reduce the cost of a paving operation.